Fix spelling in comments and documentation using codespell

Apply the utility from https://github.com/codespell-project/codespell/
to fix spelling issues in the headers under both include and interface
directories and add a file with a couple of exceptions.

The exact command line used was:

    $ codespell -w -I misc/scripts/codespell.ignore -i 3 in*

include/wx/xtitypes.h

@@ -263,7 +263,7 @@ void wxFlagsToString( wxString &s, const e& data )
 //  The first characterization is done by wxTypeKind. All enums up to and including
 //  wxT_CUSTOM represent so called simple types. These cannot be divided any further.
 //  They can be converted to and from wxStrings, that's all.
-//  Other wxTypeKinds can instead be splitted recursively into smaller parts until
+//  Other wxTypeKinds can instead be split recursively into smaller parts until
 //  the simple types are reached.
 
 enum wxTypeKind